Tropical Cyclones are organized areas of low pressure defined by wind speeds. In the Atlantic basin, we use the Saffir-Simpson Hurricane Wind Scale to predict potential wind damage from Tropical Cyclones. In a well organized storm, the strongest winds are located near the center in the most intense convection – that is the heaviest rain and thunderstorms. In well organized tropical storms and hurricanes this region is known as the “eye-wall“. The “eye-wall” forms a ring around the nearly calm “eye” region. Extreme changes in wind speed and direction are common near the center of Tropical Cyclones making them particularly dangerous.
In the outer rain bands of Tropical Cyclones, squally showers and thunderstorms are common. Intense outer rain bands can produce tornadoes. Generally speaking, tornadoes spawned by hurricanes are relatively weak (<EF2 on the Enhanced Fujita scale) and short lived, but even those can be damaging.
When a Watch or Warning is issued for Bermuda, they are timed with respect to the onset of Tropical Storm force winds (see below). However, preparations should be completed far in advance of these winds because squally showers, and high seas frequently ensue well before the Tropical Storm force winds, making preparations dangerous or impossible.
|Saffir-Simpson Hurricane Wind Scale||Based on 1-minute sustained winds|
|Tropical Storm||Winds: 34-63kts/39-73mph|
|Hurricane: Category 1||Winds: 64-82kts/74-95mph (Minimal Damage)|
|Hurricane: Category 2||Winds: 83-95kts/96-110mph (Moderate Damage)|
|Major Hurricane: Category 3||Winds: 96-112kts/111-129mph (Major Damage)|
|Major Hurricane: Category 4||Winds: 113-136kts/130-156mph (Extreme Damage)|
|Major Hurricane: Category 5||Winds: >137kts/>157mph (Catastrophic Damage)|
For reference, Hurricane Emily(1987) hit Bermuda as a category 1, Hurricane Dean(1989) hit Bermuda as a category 2, and Hurricane Fabian(2003) hit Bermuda as a category 3. Remember that no storm is the same! Each storm has its own personality and will behave in its own unique way, so it is important to stay up-to-date with the latest advisory products issued by the Bermuda Weather Service, Bermuda Emergency Measures Organization, and the National Hurricane Center.